Germination of Cotton Seed in Relation to Temperature1

The effect of constant temperature on the germination rate and percentage of two cotton seed lots was determined using a thermogradient plate. A gradient of 10 oC to 40 oC was established across the plate so that temperatures changed 2 oC for each 5 cm increment in length, resulting in sixteen different temperature treatments. The optimal temperature zone for germination was 28 oC to 30 oC. As temperature decreased from the optimal zone, the rate of germination also decreased but germination percentages during the 10-day period were significantly lower only below 20 oC. As temperature increased above the optimal zone, the rate of germination decreased and the percentage of germination sharply decreased above 32 oC 34 oC. As expected, high quality cotton seed performed better than medium quality seed for a low temperature range (16 oC to 22 oC), but the most intriguing results were observed for the high temperatures range (36 oC to38 oC). The germination of medium quality cotton seed was consistently higher than for high quality seed, especially at 38 oC after the second day of evaluation. This response has not been reported in the literature and further research is needed to better understand the germination physiology of cotton seed at high temperatures.